It’s truffle season again. In the Perigord, grizzled Frenchmen scour the forests using specially-trained female pigs or dogs to sniff out the rare black fungi growing from the roots of various tree species. In Piedmont, Italy, a similar hunt is under way for the even more esteemed white truffle. According to The Daily Beast, these little buggers can fetch an average of $3,500 a pound in a good economy (in ’09, the price for white truffles dropped to $1,800 to $2,500 a pound), making them one of the most expensive ingredients on earth.

In celebration of all this fungal goodness, Alexander’s Steakhouse in San Francisco is offering a nine-course truffle dinner for $390, through early 2011. Inside Scoop SF also tells us that for another $110, the restaurant will pair the wines for you. The Japanese-inflected meat temple opened last month in the buzzing SoMa neighborhood, but the sister location in the Silicon Valley is offering the same special.

Why are people willing to spend so much cash on a glorified foraged mushroom that smells like male pig pheromones? Gourmands will tell you the essence of the homely truffle elevates everything from scrambled eggs to pasta to euphoric levels. And truffles are supposedly an aphrodisiac (the scent of swine sex hormones, and all). Fortunately, a little of the pungent fungi goes a long way, and Alexander’s uses a total of 15 grams (roughly half-an-ounce) of black and white truffles on its special menu.